I've recently had my attention drawn to the USNS MERCY (and upon subsequent research, her sister, COMFORT). So I looked up the story of the United States Naval Hospital Ship, MERCY.
First things first, here's what I found out about why MERCY is written in caps. Ship names: The following are writers' guidelines: Names of specific ships and other vessels are both capitalized and italicized (or capitalized entirely - "all caps" - in text documents denying italics such as email, use of a mechanical typewriter.) ... If used in place of a name, the number should be italicized.
The first MERCY was originally named SARATOGA and was built by William Cramp & Sons, Philadelphia, PA. as an Army troop transport in the first nine months of World War I. The ship was renamed MERCY and converted into a hospital ship.
Commissioned on the 24th of January, 1918, MERCY operated in the Chesapeake Bay, having her homeport in Yorktown, Virginia, attending war wounded and transporting from other ships to the shore hospitals.
MERCY made four trips to and from France. She returned 1,977 casualties by the following March. For the next 15 years MERCY served off the East Coast back in Philadelphia. She was in reduced commission from December 1924 until September 1926. She was loaned to the Philadelphia branch of the Public Relief Administration in March 1934.
The second MERCY was a troop ship built by Consolidated Steel Corp., Wilmington, CA, started on February 4, 1943. Launched under 2 months later on March 25, 1943. MERCY was converted by Los Angeles Shipbuilding & Drydocking Co., San Pedro, CA and commissioned on August 7, 1944, staffed by the Army's 214th Station Hospital.
MERCY was transferred to the U.S. Army on June 20, 1946 for further service as a hospital ship. MERCY received two battle stars for World War II service. She was struck from the Navy List on the 25th of September, 1946 after just three and a half years.
The third and current MERCY was built as an oil tanker, SS WORTH, by National Steel and Shipbuilding Co., San Diego , in 1976. Starting in July of 1984, the ship was renamed and converted to a hospital ship by the same company. Launched on July 20, 1985 and USNS MERCY was commissioned on November 8, 1986.
The primary mission for MERCY is to provide rapid, flexible, and mobile acute medical and surgical services to support military operations. Secondarily, she provides mobile surgical hospital service for use by US Government agencies in disaster and humanitarian relief.